关于随机函数的问题，求教。

[Camel_J]

extern int roll_count;

int roll_n_dice(int dice, int sides);

#include"diceroll.h"
#include<stdio.h>
#include<stdlib.h>

int roll_count = 0;

static int rollem(int sides)
{
	int roll;
	
	roll = rand() % sides + 1;
	++roll_count;
	
	return roll;
}
int roll_n_dice(int dice,int sides)
{
	int d;
	int total = 0;
	
	if(sides < 2)
	{
		printf("Need at least 2 sides.\n");
		return -1;
	}
	if(dice < 1)
	{
		printf("Need at least 1 die.\n");
		return -1;
	}
	for(d = 0 ; d < dice ; d++)
		total += rollem(sides);
		
	return total;
}

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include"diceroll.h"

int main(void)
{
	int dice, roll;
	int sides;
	int status;
	
	srand((unsigned int)time(0));  // 请问这里的srand()是否没什么用，如果有用，在这个程序什么地方用到?如何使用？
	printf("Enter the number or sides per die,0 to stop.\n");
	while(scanf("%d",&sides) == 1 && sides > 0)
	{
		printf("How many dice?\n");
		if(status = scanf("%d",&dice) != 1)
		{
			if(status == EOF)
				break;
			else
			{
				printf("You should have entered an integer.");
				printf(" Let's begin again.\n");
				while(getchar() != '\n')
					continue;
				printf("How many sides?Enter 0 to stop.\n");
				continue;
			}
		}
		roll = roll_n_dice(dice,sides);
		printf("You have rolled a %d using %d %d-sides dice.\n",
				roll,dice,sides);
		printf("How many sides?Enter 0 to stop.\n");	
	}
	printf("The rollem() function was called %d times.\n",roll_count);
	printf("GOOD FORTUNE TO YOU!\n");
	
	return 0;
}

[paschen]

srand只是初始化随机数种子，一般运行一次就可以了，可以在程序开始时运行，或者第一次需要随机数的时候运行 http://en.cppreference.com/w/c/numeric/random/srand

[mstlq]

http://zh.cppreference.com/w/cpp/numeric/random/rand http://zh.cppreference.com/w/cpp/numeric/random/srand 请将上面两个链接的内容完整地读一下，并注意这句话——每次以同一 seed 播种 rand() 时，它必须产生相同的值数列。

[赵4老师]

C:\Program Files\Microsoft Visual Studio 10.0\VC\crt\src\rand.c

/***
*rand.c - random number generator
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       defines rand(), srand() - random number generator
*
*******************************************************************************/

#include <cruntime.h>
#include <mtdll.h>
#include <stddef.h>
#include <stdlib.h>

/***
*void srand(seed) - seed the random number generator
*
*Purpose:
*       Seeds the random number generator with the int given.  Adapted from the
*       BASIC random number generator.
*
*Entry:
*       unsigned seed - seed to seed rand # generator with
*
*Exit:
*       None.
*
*Exceptions:
*
*******************************************************************************/

void __cdecl srand (
        unsigned int seed
        )
{
        _getptd()->_holdrand = (unsigned long)seed;
}


/***
*int rand() - returns a random number
*
*Purpose:
*       returns a pseudo-random number 0 through 32767.
*
*Entry:
*       None.
*
*Exit:
*       Returns a pseudo-random number 0 through 32767.
*
*Exceptions:
*
*******************************************************************************/

int __cdecl rand (
        void
        )
{
        _ptiddata ptd = _getptd();

        return( ((ptd->_holdrand = ptd->_holdrand * 214013L
            + 2531011L) >> 16) & 0x7fff );
}